Inclusion Criteria:

- Healthy non-smokers

- Age <35 years (younger group)

- Aged matched to COPD patients (older group)

- Normal spirometry

- Subjects are able to give informed consent

- Healthy smokers

- Age <35 years (younger group)

- Aged matched to COPD patients (older group)

- Normal spirometry

- Subjects are able to give informed consent Stable COPD patients: Stage I-IV
according to the GOLD guidelines (3), (9)

- Current and/or ex-smokers with no less than 10 pack-year smoking history

- The subjects are able to give informed consent COPD patients with acute
exacerbation: Stage I-IV according to the GOLD guidelines (3), (9)

- Exacerbation of COPD defined as "an event in the natural course of the disease
characterised by a change in the patient's baseline dyspnoea, cough and/or
sputum beyond day to day variability sufficient to warrant a change in
management" (9)

- Current and/or ex-smokers with no less than 10 pack-year smoking history

- The subjects are able to give informed consent Asthma patients

- Patients diagnosed with asthma

- The subjects are able to give informed consent Bronchiectasis patients

- Patients with CT-confirmed bronchiectasis

- The subjects are able to give informed consent Cystic fibrosis patients

- Patients diagnosed with cystic fibrosis

- The subjects are able to give informed consent

Exclusion Criteria:

- Healthy non-smokers and smokers

- Upper respiratory infection within the last 4 weeks.

- Subjects who have received research medication within the previous one month.

- Subjects unable to give informed consent.

- Any psychiatric condition rendering the patient unable to understand the nature,
scope and possible consequences of the study Stable COPD patients

- Patients who have had an exacerbation which required treatment with oral
steroids during the last 2 months prior to the visit

- Upper respiratory infection within the last 4 weeks

- Subjects who have received research medication within the previous one month

- Subjects unable to give informed consent

- Any psychiatric condition rendering the patient unable to understand the nature,
scope and possible consequences of the study COPD patients with acute
exacerbation

- Subjects who have received research medication within the previous one month

- Subjects unable to give informed consent

- Any psychiatric condition rendering the patient unable to understand the nature,
scope and possible consequences of the study Asthma

- Upper respiratory infection within the last 4 weeks

- Subjects who have received research medication within the previous one month

- Subjects unable to give informed consent.

- Any psychiatric condition rendering the patient unable to understand the nature,
scope and possible consequences of the study.

- Bronchiectasis and cystic fibrosis

- Subjects who have received research medication within the previous one month.

- Subjects unable to give informed consent.

- Any psychiatric condition rendering the patient unable to understand the nature,
scope and possible consequences of the study.